It's basically Nightmare on Elm Street rules. If you die in Walter's world, you die in real life. This is demonstrated with all the previous Sacraments. While Eileen travels with you, she's unconscious in the hospital. When you meet Cynthia, she's asleep on the subway. When she dies, she dies for real.

But how can she die in reality? Well, from the memos, I know that her soul is sucked down by otherworld so it cant return to her body(Souls will live forever, they will haunt that realm as spirit)... So A body without soul = dead. OK. But why bodies also get heavily damaged? Like Jasper. His body is burned out. It is kinda like his burning soul tried to enter his body but flames fired his own body from burning soul . It cant be possible. How can his body get burned?

A person`s real body can not get heavily damaged by dreams, by Astral Projection too.